1. Field of the Invention
The present invention relates to a printing technology in an ink-jet printer, and more particularly, an ink set comprising a recording composition and a treating composition with feathering and color bleed inhibited for high image quality, an image forming process and an image forming apparatus using the same, and a print.
2. Description of the Related Art
The ink-jet recording process, wherein an image is recorded using droplets of a recording composition containing a colorant, is advantageous in its simple printing mechanism without noise.
The image recording process has a problem in that character blurring (hereinafter referred to as feathering) may occur in accordance with a combination with a recording medium, which causes deterioration in image quality. In order to solve this problem, there has been an attempt to reduce the feathering by inhibiting the permeation of an ink (recording composition). However, this process has defects in that the hand is stained or image defects occur when the print is touched by the hand after printing since the recording composition has poor dryness.
Also, when a color image is printed, since inks of different colors are overlapped one upon another, the color inks are mixed or blurred in the boundary between the colors (hereinafter referred as color bleed), thereby deteriorating image quality. There has an attempt to reduce the color bleed by increasing the permeation of the recording composition. However, this process has defects in that the colorant gets into the recording medium, thereby causing reduction in image density, or a large amount of the recording composition passes through the back of the recording medium, which badly affects two-sided printing (printing on both sides of a sheet).
For these circumstances, there is demand for development of an image forming process to solve the foregoing problems and increase image quality.
For the above problems, it has been proposed a process using a recording composition containing a colorant in combination with a treating composition containing a component which can react with the colorant to form aggregates in a single body. For example, there is known a process using a recording composition in combination with a treating composition containing a water-soluble resin having at least one of carboxyl group or anhydride thereof, or sulfonate group. Also, a process using a recording composition in combination with a color free or light color liquid containing a compound at least two cationic groups in a molecule or a process using a recording composition in combination with a liquid composition comprising polyallylamine and glycerine is disclosed.
However, according to these processes, since such a high molecular reactive component is contained in the state dissolved in the treating composition, when it is added in a large amount, viscosity increase may occur, causing ejection failure from a recording head. Therefore, the content of the reactive component should be lowered and consequently, the viscosity change (increase) upon reaction with a colorant is reduced, whereby feathering inhibition effect is insignificant.
Also, there are proposed a process using a recording composition in combination with a color free or light colored liquid containing a polyhydric metal salt, a process using a recording composition in combination with a color free or light colored liquid containing a quaternary ammonium salt or amine salt, and a process using a recording composition in combination with a color free or light colored liquid containing a quaternary ammonium salt or amine salt and polyhydric alcohol.
However, in the process using a polyhydric metal salt or amine compound, these compounds may be added in a large amount but the size of the added molecule is small and hardly forms big aggregates even when reacted with the colorant. Therefore, the viscosity change upon reaction with a colorant is large enough, whereby feathering inhibition effect is insignificant.
In order to further improve image quality, a process using a treating composition containing fine particles as a component reactive with a colorant contained in a recording composition is proposed. For example, an ink-jet recording process is disclosed, wherein a color free liquid containing silica fine particles is adsorbed on a recording medium and a non-aqueous recording composition containing oil black (for example, Japanese Patent Application Laid-Open (JP-A) No. 4-259590). Also, a reaction solution containing an emulsion of a cation having a part of ability of UV absorption and/or light stabilization (for example, WO 2000-06390), or a solution containing fine particles, or fine particles and a binder polymer (for example, JP-A No. 6-92010) is disclosed. Further, a substantially color free liquid composition containing an anionic metal oxide colloid (for example, JP-A No. 11-228890), a light colored or white liquid composition comprising water-insoluble fine particles, a water-soluble organic solvent and water (for example, JP-A No. 2000-34432), a translucent white ink composition mainly comprising an inorganic oxide pigment (for example, JP-A No. 2001-171095), and a liquid composition comprising fine particles reactive with a colorant (for example, JP-A No. 2001-199149) are disclosed. In addition, a liquid composition comprising fine particles, which are surface-charged with a polarity opposite to that of a recording composition, in the state of a dispersion (for example, JP-A No. 2001-199150 and JP-A No. 2001-199151) is disclosed.
Since the liquid containing fine particles comprises the reactive fine particles in the state of a dispersion, it may inhibit increase in the viscosity and contain a large amount of the reactive component, as compared to the treating composition for dissolving a polymer as described above. Also, since the fine particles have a big particle size, as compared to the polyhydric metal salt and the like, when the dispersion is break by the reaction with a colorant, they may form big aggregates. As a result, the viscosity increases, migration of the colorant is inhibited and the feathering is improved. However, as the requirements for high image quality are strict, there is still demand for improvement of these processes.
Meanwhile, in order to produce a print with good image quality by using a recording composition in combination with a treating composition containing a component to aggregate a colorant in the recording composition, it should be necessary to make the adsorbed amount of the treating composition greater than the adsorbed amount of the recording composition. When using the treating composition, the liquid amount applied on the paper is increased by the liquid amount of the treating composition, as compared to the printing using only the recording composition. Therefore, the printed paper may swollen or cockled, or the feathering and color bleed are worsened since a large amount of liquids is applied on the paper at once.
For example, according to the JP-A No. 2001-199150, it is preferable that the mixture formed by mixing the recording composition containing a colorant and the treating composition containing fine particles in a weight ratio of about 1:1 has a pH where at least the colorant aggregates. However, when the two liquids are mixed in a weight ratio of about 1:1, the amount of the adsorbed liquid is 200% of the adsorbed amount of the recording composition along. Further, when the recording composition is applied to attain a sufficient concentration, the adsorbed amount increases, which may cause color bleed, feathering, and paper cockling.
Also, the JP-A No. 2001-199150 describes that it is preferable that the mixture formed by mixing the recording composition containing a colorant and the treating composition containing fine particles in a weight ratio of about 1:1 has a pH where at least the colorant aggregates. However, it does not include a description considering the isoelectric point of the component reactive with the colorant and the un-reacted component reactive with the colorant.
As described above, when the colorant contained in the recording composition and the component contained in the treating composition have a polarity opposite to each other, upon mixing of the recording composition with the treating composition, the colorant is adsorbed to the component reactive with the colorant to form aggregates. However, at this point, not all the colorant and the component reactive with the colorant react.
For example, about ⅓ of the mixed colorant and the fine particles contained in the treating composition aggregate by the reaction and the remaining ⅔ of the colorant permeates into the paper without reaction and is fixed. However, when it is applied on a paper with low permeation rate, the ink may be flow out into the adjacent image area, causing bleed (for example, JP-A No. 2002-201385).
According to the JP-A No. 2002-201385, the foregoing problems can be solved by adding a cationic compound to the treating composition so that it rakes the colorant molecule upon mixing, thereby restricting the location, whereby high color development, bleed inhibition and water resistance can be improved.
However, cationic polymers or oligomers which are mentioned as an example of the cationic compound, when added to the treating composition, may cause deterioration of storage stability of the treating composition and viscosity increase. A cationic surfactant lacks power to fix the colorant, as compared to the cationic polymers or oligomers and thereby, shows low and insufficient improving effect of high color development, bleed inhibition and water resistance of a print. Therefore, there is still great demand for storage stability of the treating composition and sufficiently high image quality of a print.